Goodwill has not treated Corporate America so well lately.

Impairment of goodwill—more cynically known as “writing down the value of assets that aren’t worth what you thought”—rose sharply among the S&P 500 last year. Total impairment stood at $30.78 billion, compared to $12.02 billion in 2014. Average impairment among the S&P 500 jumped from $26.4 million in 2014 to $67.7 million last year.

The good news is that only 40 companies in the S&P 500 reported any goodwill impairment at all last year. The bad news: that number is still up 11 percent from 2014, when 36 companies disclosed an impairment charge.

A quick refresher for any non-accountants or analysts reading this post: goodwill is the value places on an asset above its tangible worth. For example, if a software company with $1 million in “hard” assets (computers, property, cash, receivables) is acquired for $10 million, that implies $9 million in goodwill—the value placed on intangible assets such as software patents, customer loyalty, and talented personnel.

Impairment occurs when the company decides (often reluctantly, and after a two-step test to determine impairment) that those intangible assets aren’t worth the stated value. Maybe those patents are invalidated, or long-time customers leave, or employees quit. Suddenly that software company acquired for $10 million is floundering, and that new parent writes down the goodwill value from $9 million to something lower; the exact number depends on just how bad the floundering is.

The mother of all impairments happened in 2003, when Time-Warner took a $45.5 billion impairment on its acquisition of AOL (which Time-Warner had acquired for $103.5 billion just two years earlier). More recently, one of the largest impairments in 2015 happened at Yahoo; it wrote down $4.4 billion in goodwill due to “a combination of factors, including a sustained decrease in our market capitalization in fourth quarter of 2015 and lower estimated projected revenue and profitability in the near term.”

That $4.4 billion was allocated across North America, Latin America, and European operations, plus a separate write-down of $230 million for Tumblr, which Yahoo acquired in 2013 for $1.1 billion, including a press release promising “not to screw it up.”

The next seven companies behind Yahoo, all reporting impairments of $1 billion or more, were in the oil & gas sector—so no surprise there, given how troubled that sector has been with falling oil prices.

You can explore more goodwill impairments yourself on our Normalized Data or Company in Detail pages. Be sure to read our Guide to Analyzing Goodwill and try our Goodwill & Intangibles Excel Template, too.